The aims of the proposed research are to examine the expression of antibody diversity during B cell development, in particular for antigens under immune response (Ir) gene control; to examine the susceptibility of B cells at different stages of maturation to Ir gene regulation; to examine carrier-dependent effects on B cell subset selection and stimulation;and to examine whether genes in the mouse major histocompatibility complex (H-2) influence or regulate B cell subset selection and idiotypic expression. The long-term objectives are to understand the mechanisms which generate antibody diversity during ontogeny and the mechanisms by which H-2 recognition affects cellular interactions, selective expression of the B cell idiotypic repertoire, and Ir gene regulation of the immune response.